Conformational Analysis of XA and AX Dipeptides in Water by Electronic Circular Dichroism and 1H NMR Spectroscopy
| Autor: | Thomas J. Measey, Reinhard Schweitzer-Stenner, Ravi Doddasomayajula, Kai Griebenow, Fatma Eker, Andrew Hagarman, Isabelle Dragomir |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Circular dichroism
Magnetic Resonance Spectroscopy Protein Conformation Stereochemistry Population Electrons Peptide Spectral line Residue (chemistry) Materials Chemistry Physical and Theoretical Chemistry education Polyproline helix Alanine chemistry.chemical_classification education.field_of_study Circular Dichroism Temperature Water Dipeptides Hydrogen-Ion Concentration Surfaces Coatings and Films Crystallography chemistry Proton NMR Thermodynamics |
| Zdroj: | The Journal of Physical Chemistry B. 110:6979-6986 |
| ISSN: | 1520-5207 1520-6106 |
| DOI: | 10.1021/jp0561625 |
| Popis: | We measured the temperature-dependent electronic circular dichroism (ECD) spectra of AX, XA, and XG dipeptides in D2O. The spectra of all XA and AX peptides indicate a substantial population of the polyproline II (PPII) conformation, while the ECD spectra of LG, KG, PG, and AG were found to be quantitatively different from the alanine-based dipeptides. Additional UV absorption data indicate that the ECD spectra of the XG peptides stem from electronic coupling between the peptide and the C-terminal group, and that spectral differences reflect different orientations of the latter. We also measured the 1H NMR spectra of the investigated dipeptides to determine the 3JHalphaNH coupling constants for the C-terminal residue. The observed temperature dependence of the ECD spectra and the respective room-temperature 3JHalphaNH coupling constants were analyzed by a two-state model encompassing PPII and a beta-like conformation. The PPII propensity of alanine in the XA series is only slightly modulated by the N-terminal side chain, and is larger than 50%. As compared to AA, XA peptides containing L, P, S, K V, E, T, and I all cause a relative stabilization of the extended beta-strand conformation. The PPII fractions of XA peptides varied between 0.64 for AA and 0.58 for DA, whereas the PPII fractions of AX peptides were much lower. From the investigated AX peptides, only AL and AQ showed the expected PPII propensity. We found that AT, AI, and AV clearly prefer an extended beta-strand conformation. A quantitative comparison of AA, AAA, and AAAA revealed a hierarchy AAAAAAA approximately AA for the PPII population, in agreement with predictions from MD calculations and results from Raman optical activity studies (McColl et al. J. Am. Chem. Soc. 2004, 126, 5076). |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|